Abstract: The pipelines of nuclear power units are prone to vibration due to external and internal influences. Long-term operation will increase the risk of pipeline rupture and endanger the safe operation of the unit. The commonly used supports and hangers have limited vibration reduction effects and may change the natural frequency of the pipeline and cause resonance. This paper designs a double dynamic vibration absorber (DDVA) for reducer pipe vibration reduction. The optimal design conditions are determined through theoretical derivation, and the mass, stiffness and damping ratio are calculated using the optimal design conditions. The structure of DDVA is designed in combination with the application scenario to achieve easy installation. This paper conducts modal analysis and harmonic response analysis on variable diameter pipelines, and finally conducts vibration tests on variable diameter pipelines in nuclear power plants. The field test results show that: near 49.8 Hz, the vertical and horizontal vibration absorption efficiency of DDVA at points 2 and 3 on the pipeline reaches more than 85%. Near 100 Hz, the vertical and horizontal vibration absorption efficiency of DDVA installed with metal rubber is increased by about 60% at point 2, and the vertical and horizontal vibration absorption efficiency of point 3 is increased by about 50% compared with DDVA without metal rubber installed. This proves that metal rubber materials effectively enhance the vibration absorption effect of dynamic vibration absorbers. The research results have significant engineering significance for vibration control of nuclear power pipelines.